This invention relates to a method for controlling a transfer case and more particularly, to a method for controlling a transfer case within a four wheel drive vehicle which provides an improved response by monitoring and reacting to the gradient or the rate of change of the position of the vehicle""s throttle.
Four-wheel drive vehicles typically include a transfer case which selectively transfers torque and power from the vehicle""s input shaft to a front and a rear driveshaft, thereby selectively rotating the front and rear driveshafts. The transfer case includes a conventional electromagnetic clutch assembly which typically and selectively transfers torque from a primary driveshaft (e.g., the rear driveshaft) to a secondary driveshaft (e.g., the front driveshaft), thereby reducing the torque provided to the primary driveshaft and increasing the torque provided to the secondary driveshaft. The clutch assembly is typically and communicatively coupled to a controller and/or control system which determines the amount of torque that is to be provided to the front and rear driveshafts based upon vehicle sensory data, and which generates a command signal to the clutch assembly, thereby controlling the amount of torque which is provided to front and rear driveshafts. Particularly, in order to provide torque and traction to the front and rear wheels of the vehicle and to avoid relative slip between the front and rear wheels, the transfer case controller and/or control system typically monitor the speed of both the front and rear driveshafts and the position of the vehicle""s throttle (i.e., xe2x80x9cthrottle positionxe2x80x9d).
While these types of prior systems provide sufficient traction and control to the front and rear wheels of a vehicle in many situations, they suffer from some drawbacks. One drawback associated with these prior systems is that they typically monitor and react to the throttle position (i.e., the currently sensed or measured position of the throttle), and do not monitor the rate of change or gradient of the throttle position. Hence, these systems do not adequately account for or react to relatively rapid movements of the vehicle""s throttle, which are of a relatively short duration (e.g., short bursts of acceleration or deceleration). In these types of situations, prior systems often allow slippage to occur between the front and rear wheels of the vehicle, or cause and/or suffer from undesirable noise and vibration harshness (xe2x80x9cNVHxe2x80x9d) difficulties, which are perceived by the operator and/or passengers of the vehicle.
There is therefore a need for a method and an apparatus for controlling a transfer case within a four-wheel drive vehicle which provides an improved response by monitoring and reacting to the rate of change of the position of the vehicle""s throttle.
A first advantage of the invention is that it provides a method and an apparatus for controlling a transfer case within a four-wheel drive vehicle which overcomes at least some of the previously delineated drawbacks of the prior systems, devices, and/or methods.
A second advantage of the invention is that it provides a method and an apparatus for controlling a transfer case within a four-wheel drive vehicle which monitors and desirably reacts to the rate of change of the position of the vehicle""s throttle.
A third advantage of the invention is that it provides a method and an apparatus for controlling a transfer case within a four-wheel drive vehicle which is effective to substantially prevent slippage between the front and rear wheels of the vehicle during short bursts of acceleration or deceleration in a manner which does not result in undesirable NVH problems.
According to one aspect of the present invention, a system for controlling a transfer case is provided. The transfer case is operatively disposed within a four-wheel drive vehicle of the type having a selectively positionable throttle and a front and a rear driveshaft. The transfer case is effective to selectively transfer torque to the front driveshaft and to the rear driveshaft. The system includes a sensor which senses a first and a second position of the throttle and which generates at least one signal representing the sensed first and second position; and a controller which is communicatively coupled to the transfer case and to the sensor. The controller receives the at least one signal and utilizes the at least one signal to calculate a rate of change of throttle position. The controller is further adapted to selectively generate an output signal based upon the rate of change of throttle position, the output signal being effective to selectively control the torque which is transferred to the front and rear driveshafts.
According to a second aspect of the present invention, a method for controlling a transfer case is provided. The transfer case is operatively disposed within a four wheel drive vehicle of the type having a selectively positionable throttle which changes position by a certain amount during an interval of time, a front driveshaft and a rear driveshaft. The transfer case is adapted to selectively provide torque to the front driveshaft and the rear driveshaft. The method includes the steps of measuring the certain amount; using the certain amount to calculate a rate of change of the position of the throttle; comparing the calculated rate of change of the position of the throttle to a rate threshold value; and selectively providing a boost torque signal to the transfer case when the rate of change of the position of the throttle exceeds the rate threshold value, the boost torque signal being effective to alter the torque provided to the front driveshaft and the rear driveshaft.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.